Geranylgeranyl pyrophosphate (GGPP) synthase, also known as geranylgeranyl-diphosphate synthase, farnesyl transferase and geranylgeranyl synthetase is a key enzyme in plant terpenoid biosynthesis. The final product, GGPP, is the key precursor of several holoterpenoids such as carotenoids and meroterpenoids. One fate of GGPP is conversion to phytoene by phytoene synthase, the first committed step in carotenoid biosynthesis. Although not specific to carotenoid biosynthesis, GGPP synthase may be important in determining the total catorenoid content of a specific tissue. Expression of the GGPP synthase gene is strongly induced during the chloroplast to chromoplast transition which occurs in ripening peppers which have a high carotenoid content (Kuntz, M., et al. (1992) Plant J. 2:25–34).
GGPP also serves as precursor in the formation of defense-related substances like the phytoalexin casbene in castor bean and the diterpene phorbol which acts as a toxin against herbivores. GGPP is also a precursor of the important phytohormone gibberellin which regulates a variety of physiological processes that include initiation of seed germination, stimulation of stem elongation, stimulation of flowering/bolting and regulation of leaf/fruit senescence.
In animal systems, the importance of the enzyme GGPP synthase is demonstrated by the lethality of nonsense mutations in the locus that encodes the enzyme in Drosophila (Lai et al. (1998) Genetics 149:1051–1061). In plant systems, GGPP serves as precursor to many important metabolites that the enzyme responsible for its synthesis, GGPP synthase, appears to be an attractive target for herbicide discovery and design.
At least 6 different GGPP synthases have been identified in Arabidopsis thaliana. Beside differences in the amino acid sequence of the proteins and the nucleotide sequence of their genes, GGPP synthases accumulate in different subcellular compartments (Zhu, X. F., et al. (1997) Plant Mol. Biol. 35:331–341).
Manipulation of the corn gene in endosperm could result in increased xanthophyll content, which has value as coloring agent in poultry feed